In the lighting technology sector it is very common to use decorative glass which, in addition to constituting an ornamental element influencing the aesthetic effect of the finished product, performs the dual function of ensuring improved diffusion of the light and protecting the light source which generally consists of a bulb.
Many of the bulbs which are currently available are associated with lamp holders; however, the possibility of directly associating lamp holder and decorative glass does not exist.
In fact, in the case where the glass has a thread, the latter is formed on a portion of their outer surface and, since the lamp holders may at best be also threaded externally, it becomes necessary to use an additional metal or plastic element which is machined internally and onto which the glass can be screwed or engaged in bayonet fashion. The limitation of this solution consists in the fact that complex processing of the glass must be performed using costly moulds and at high pressures in order to achieve optimum results. Moreover, the glass must have a fairly large thickness and this limits considerably the areas in which it may be used.
In other cases, the glass is supported by a spring which, after being forced into an opening formed in the surface, expands so as to exert a pressure on the walls of the opening. However, the firmer the fastening, the more difficult it will be to extract the spring from the opening; if, on the other hand, it is ensured that the spring can be extracted more easily, there is the risk that during use the spring may come out on its own. A very tight fastening furthermore may result in possible damage to the glass when removing the spring and generally this type of constructional solution worsens significantly the aesthetic effect of the assembly.
As an alternative, finally, the glass may be supported by a ring nut which can be screwed onto the lamp holder and which can be inserted inside the glass and perform its function making use of the weight of the glass, or can be glued thereto.
It is obvious, however, that the first possibility is not feasible whenever the glass has a closed, or at least a tapered shape, whereas the second possibility creates irregular reflections and shadows which are aesthetically unacceptable, in addition to not providing satisfactory guarantees as to strength.